Support means for ceramic shell moulds

ABSTRACT

A CERAMIC SHELL MOLD IS PARTIALLY IMMERSED IN A FLUIDIZED BED OF GRANULAR REFRACTORY MATERIAL. THE BED IS THEN DEFLUIDIZED SO THAT THE SHELL MOLD IS FIRMLY EMBEDDED IN READINESS TO RECEIVE A CHARGE OF MOLTEN METAL.

Sept. 20, 1971 R. P. CHAPMAN EIAL 3,605,869

SUPPORT MEANS FOR CERAMIC SHELL MOULDS 3 Shoots-Shoot 1 Filed Oct. 22, 1969 Sept. 20, 1971 R. P. CHAPMAN ETAL 3,605,869

SUPPORT MEANS FOR CERAMIC SHELL MOULDS 3 Sheets-Sheet 2 Filed Oct. 22, 1969 Sept. 20, 1971 R. P. CHAPMAN l-n'm. 3,605,869

SUPPORT MEANS FOR CERAMIC SHELL MOULDS Filed 001:. 22, 1969 :5 Sheets-Sheet} United States Patent 3,605,869 SUPPORT MEANS FOR CERAMIC SHELL MOULDS Roland P. Chapman, Redditch, and Barry F. Irving,

Highley, England, assignors to British Leyland (Austin- Morris) Limited (formerly The British Motor Corporation Limited), Longbridge, Birmingham, England Filed Oct. 22, 1969, Ser. No. 868,528 Claims priority, application Great Britain, Nov. 9, 1968, 53,201/ 68 Int. Cl. B22d /04 U.S. Cl. 164-324 4 Claims ABSTRACT OF THE DISCLOSURE A ceramic shell mold is partially immersed in a fluidized bed of granular refractory material. The bed is then defluidized so that the shell mold is firmly embedded in readiness to receive a charge of molten metal.

This invention relates to methods of, and means for, supporting ceramic shell moulds while molten metal is poured into them, as in the process of investment casting.

In the process of investment casting, a wax pattern of the article which is to be cast in metal is first produced in an injection-moulding die, and is then subjected to a sequence of operations which result in its receiving (in addition to repeated coatings of slurry) several coatings of powdered ceramic material. The ceramic shell progressively formed in that way is dried, the wax is removed by melting, and then the shell is fired to produce the finished shell mould which is now ready for receiving its charge of molten metal.

As the ceramic shell mould is rather thin-walled, it is necessary to arrange for it to be adequately supported so that it is able to withstand the charge of molten metal. This may be accomplished by manually packing a granular refractory material around the mould, but this expedient is hardly appropriate in the case of an automatic flow-production investment casting plant.

According to this invention a method of supporting a ceramic shell mould while it receives a charge of molten metal comprises: fiuidizing a bed of a granular refractory material, partially immersing the shell mould in the fluidized bed, and then de-fiuidizing the bed so that the shell mould is held firmly embedded in readiness to receive the charge of molten metal. More specifically, the preferred method comprises initially positioning the ceramic shell mould above the fluidized bed, and then raising the bed to effect the partial immersion of the shell mould.

In order to enable the invention to be employed in an automatic flow-production investment casting plant, a fluidized bed conveyor incorporating the invention has been devised. It comprises: two pairs of horizontal rails spaced apart vertically to form top and bottom rail tracks; a plurality of tanks, each containing a bed of granular refractory material, mounted for indexing movement along the tracks; a pair of automatic lifts, each incorporating a section of the rail tracks, located at opposite ends of the tracks and arranged to operate in phase with each other; separate indexing means pertaining to the respective tracks; and means effective automatically to fluidize the bed in a tank while it is being raised from the bottom track by one of the lifts.

Referring to the accompanying drawings:

FIG. 1 is a schematic broken side elevation of a fluidized bed conveyor incorporating the invention, and enabling it to be employed in an automatic flow-production investment casting plant; and

FIGS. 2, 3 and 4 are fragmentary perspective views depicting various stages in the operation of the fluidized bed conveyor shown in FIG. 1.

Patented Sept. 20, 1971 The fluidized bed conveyor illustrated, which consistitutes part of an automatic investment casting plant, has an open frame 1 of rectangular box-like form. This frame incorporates two pairs of horizontal rails 2 and 3, spaced apart vertically to form top and bottom tracks 4 and 5 upon which tanks 6 containing sand are individually supported by rollers 7 that run on the respective rails. At the loading end of the conveyor there is an automatic lift 8 by which each of the tanks 6, in turn, is raised from the bottom track 5 to the level of the top track 4. At the unloading end of the conveyor there is an automatic lift 9 by which each of the tanks 6, in turn, is lowered from the top track 4 to the level of the bottom track 5. The two lifts 8 and 9 are of identical construction, each comprising a section of the rail tracks supported by a pair of struts 10, and are operated pneumatically. Each lift is mounted on one end of a chain 11 that passes around idler sprockets 12, the other end of the chain being coupled to the piston of a pneumatic cylinder 13. Although the lifts 8 and 9 are operated by separate pneumatic cylinders 13, and separate chains 11, they are arranged to work in phase with each other. That is to say, they rise and descend together and are at the same level at any time.

In a manner which will be described later, the conveyor indexes the tanks 6 along the top track 4 from left to right in FIG. 1, and along the bottom track 5 from right to left. 'Either of the lifts 8 and 9 can only receive one of the tanks 6 when another tank is simultaneously moved out of the other lift.

When the conveyor indexes the tanks 6 along the bottom track 5, the lift 8 is at the level of that track (see FIG. 2). Each of the tanks 6 has a false bottom which is constituted by a porous ceramic tile 14 (FIG. 1). A bed of sand 15 rests upon this tile, and the left hand end of the tank has an air inlet located below the tile 14. This air inlet, through a taper union connection 16, becomes automatically connected to a flexible compressed air line 17 by the final stage of movement of the tank 6 onto the lift 8. The bed of sand is now fluidized by the air bubbling through it. The air escaping from the top of the bed tends to create tiny mounds on the surface of the sand, as depicted in FIGS. 2 and 3.

By means of a mechanical hand 18, which has moved downwardly along the path indicated at 19 (FIG. 1), a ceramic shell mould 20 (which is depicted as having branches 20A) has been withdrawn from a furnace in which it was fired, and is held in position over that tank 6 which is shown in FIG. 2. Although FIG. 1 indicates (at 21) part of the mechanism for operating the mechanical hand 18, this mechanism need not be described as it is not relevant to the invention.

FIG. 3 depicts the lift 8 during its ascent from the bottom track (FIG. 2) to the top track. When this lift reaches the top of its travel (FIG. 1), the shell mould 20 has become partially immersed in the fluidized sand. The bed of sand 15 is then de-fluidized, by shutting off the air supply to the line 17, and the mechanical hand 18 releases and withdraws (see FIG. 4). The shell mould 20, which is held embedded in, and firmly supported by, the sand immediately the aeration of the bed has been stopped, is now ready to receive its charge of molten metal (which is poured at another station on the top track 4).

The conveyor now indexes the tanks 6 on the top track 4. This is accomplished by a pair of pneumatic cylinders 22 disposed at opposite sides of the top track 4; a piston rod 23 of each cylinder having at its outer end an L- shaped bracket 24 that embraces the corresponding corner at the trailing end of the tank 6 which is on the lift 8. As that tank is moved, by the brackets 24, it releases itself from the air-connection 16 and pushes the other tanks on the top track 4 one stage forward, so that the endmost tank is moved onto the lift 9 simultaneously with the lift 8 becoming empty. Upon completion of the indexing, the pneumatic cylinders 22 return the brackets 24 to their starting position. The charged shell mould 20 is now removed from the tank on the lift 9, and transferred to a cooling conveyor (not shown). Both lifts 8 and 9 are then lowered to the level of the bottom trackS.

The next operation is that the tanks 6 on the bottom track are indexed from right to left in FIG. 1. This is effected by a pneumatic cylinder 25 that has the outer end of its piston rod 26 fitted with an upright plate-like bracket 27 which is engageable with the outer end of the tank 6 that has been lowered by the lift 9. As that tank is moved, by the bracket 27, it pushes the other tanks on the bottom track 5 one stage forward, so that the endmost tank is moved onto the lift 8 simultaneously with the lift 9 becoming empty. The final stage of movement of that tank onto the lift 8, as has already been explained, results in the bed of sand becoming fluidized. Upon completion of the indexing of the tanks 6 on the bottom track 5, the pneumatic cylinder 25 returns the bracket 27 to its initial position.

The arrangement is such that the total of the tanks 6 must be an odd number, and, upon completion of each indexing movement, there must always be two superposed vacant places at one end of the conveyor and a third vacant place at its other end. It is also to be noted that if, for example, the total number of the tanks 6 is nine then, at any given time, five of them are located on either the top track 4 or the bottom track 5 (as the case may be).

When the mechanical hand 18 has brought another shell mould 20 into position above the lift 8, the cycle of operations is repeated.

We claim:

1. Means for supporting a ceramic shell mould while it receives a charge of molten metal, said means comprising: two pairs of horizontal rails spaced apart vertically to form top and bottom rail tracks; a plurality of tanks, each containing a bed of granular refractory material, and

mounted for indexing movement along the tracks; a pair of automatic lifts, each incorporating a section of the rail tracks, located at opposite ends of the tracks and arranged to operate in phase with each other; separate indexing means for each track; means for automatically fluidizing the bed in a tank while it is being raised from the bottom track by one of the lifts; mechanical means Which holds the shell mould above the ascending fluidized bed so that the shell mould becomes partially immersed therein when the corresponding lift reaches the top of its travel; and means for automatically de-fluidizing the bed after the shell mould has been partially immersed therein.

2. Supporting means according to claim 1, comprising at least one pneumatic cylinder for operating said lifts, each lift being mounted on one end of a chain that passes around idler sprockets, the other end of the chain being coupled to the piston of a pneumatic cylinder.

3. Supporting means according to claim 1 in which said separate indexing means comprise a pair of pneumatic cylinders disposed at opposite sides of the top track, and a single pneumatic cylinder for advancing a tank along the bottom track.

4. Supporting means according to claim 1 in which each tank has, near its bottom, an air inlet which, through a taper union connection, becomes automatically connected to a flexible compressed air line by the final stage of movement of the tank onto that lift by which the tank ascends from the bottom to the top track.

References Cited FOREIGN PATENTS 231,747 5/1969 USSR 164-47 J. SPENCER OVERHOLSER, Primary Examiner JOHN E. ROETHEL, Assistant Examiner US. Cl. X.R. l6447, 76, 

